1. Field of the Invention
The present invention relates to optical scanner assemblies suitable for use in an imaging system which scans a laser beam across an image carrier such as a photosensitive drum to form an electrostatic latent image on the image carrier and which then transfers a toner image formed of the latent image onto a transfer medium, while the transfer medium is being moved, to form desired images thereon.
2. Description of the Related Art
The optical scanner assembly is used in an imaging system to scan a laser beam across an image carrier while sequentially changing the position of incidence of the light beam. The imaging system allows the laser beam, representative of image information and emitted from a laser light source employed such as in copiers or printers, to be adjusted appropriately and incident upon a deflector means such as a polygonal mirror. Then, the system scans the deflected light beam across the image carrier such as a photosensitive drum to form an electrostatic latent image on the surface thereof. Thereafter, the system allows the electrostatic latent image to be developed with a toner to form a toner image, which is in turn transferred onto a transfer medium such as recording paper. Furthermore, tandem imaging systems are widely known as a color imaging system for use in the color copiers or the color printers. The imaging system is adapted to have a plurality of image carriers such as photosensitive drums in tandem with one another, across each of which a laser beam is scanned to form an electrostatic latent image. The electrostatic latent image is developed with a predetermined toner to form a toner image, which is in turn transferred sequentially onto a transfer medium such as recording paper to form a color image thereon, with the medium being moved in the tandem direction of the image carriers.
A conventional optical scanner assembly of this type, employing a structure in which an optical path from the laser light source to the image carrier is formed generally in the same plane, causes the plane containing the optical path to increase in size, resulting in a large assembly. This requires a wider area for installing the imaging system. For this reason, some optical scanner assemblies are so adapted that a plane containing the optical path of an optical system leading to the deflector means for adjusting the laser light source to scan the laser beam forms an appropriate angle with respect to a plane containing the optical path of the optical system for scanning the laser beam across the image carrier.
For example, an optical scanner assembly, which employs a polygonal mirror as the deflector means, is disclosed in Japanese Patent Laid-Open Publication No. H8-244270. A laser beam emitted from a laser light source 1 (FIG. 10) such as a laser diode passes through a collimator lens 2 and a cylindrical lens 3 to be incident upon a polygonal mirror 4. The polygonal mirror 4 is rotated at an appropriate speed, thus deflecting the laser beam incident thereon. The laser beam reflected by the polygonal mirror 4 passes through an fxcex8 lens 5 to be reflected by a reflector (not shown) and a cylindrical mirror 6, and then reflected by a reflector 7 to be incident upon a photosensitive drum (not shown).
On the other hand, disclosed in Japanese Patent Laid-Open Publication No. H8-194180 is an optical scanner assembly developed in view of the problem that the optical scanner assembly having two fxcex8 lenses, used for scanning laser beams, arranged in a straight line is prevented from being made smaller in size and thus the imaging system employing the optical scanner assembly is also prevented from being made smaller in size. The optical scanner assembly comprises a rotatable polygonal mirror for reflecting a laser beam, an fxcex8 lens having two lens portions integrated vertically, and a reflective means which reflects a laser beam reflected by the rotatable polygonal mirror to pass through one of the lens portions of the fxcex8 lens and which then guides the reflected beam into the other lens portion of the fxcex8 lens. The optical scanner assembly employs the laser beam that passes through the other lens portion as a scan beam.
Also disclosed in Japanese Patent Laid-Open Publication No. H9-318894 is an optical scanner assembly having a structure adapted such that a polygonal mirror deflects and scans a laser beam to allow most of the laser beam to form an image and pass through a half mirror and a scan lens, thereafter the laser beam is returned by a return mirror to be incident upon a rotating drum.
Furthermore, disclosed in Japanese Patent Laid-Open Publication No. H9-197331 is an optical scanner assembly, which is provided with a high degree of flexibility in the layout of components constituting the optical system. The optical scanner assembly comprises a first mirror, interposed between a light source and an optical deflector, for reflecting a light beam toward the optical deflector, and a second mirror interposed between the optical deflector and a scanned body to reflect the light beam toward the scanned body. The optical scanner assembly is adapted such that the first and second mirrors are arranged so that the optical axis of the light beam incident upon the optical deflector is inclined from a direction perpendicular to the rotational axis of the optical deflector toward a sub-scan direction, with the first mirror being located farther away from the optical deflector than the second mirror.
The optical scanner assemblies disclosed in Japanese Patent Laid-Open Publication Nos. H8-244270, 8-194180, and 9-318894 have the layout of the optical path leading from the laser light source to the deflector means substantially in the same plane. This requires a wide area for arranging the optical system leading from the laser light source to the deflector means, leaving the possibility of increasing in size of the optical scanner assembly. In addition, the optical scanner assembly disclosed in the Japanese Patent Laid-Open Publication No. H9-197331 allows a light beam to be inclined from a direction perpendicular to the rotational axis of the polygonal mirror to the sub-scan direction and thus to be incident forwardly upon a reflective surface of the polygonal mirror. However, the laser light source is arranged away from the deflector means to ensure the optical path length from the laser light source to the deflector means. This causes the optical path from the laser light source to the deflector means to spread in a plane, which therefore requires a wide area for accommodating the optical path and thus prevents the optical scanner assembly from being made smaller in size.
The optical members constituting the scan optical system and mounted in position need to remain unchanged to ensure the predetermined optical performance. For this reason, the brackets for mounting the optical members are formed of a metal plate or the like that is resistant to deformation. On the other hand, a faster capability of or use of color in imaging systems such as copiers or printers has required these days a plurality of laser beams or a plurality of units for laser beams. The plurality of laser beams or units makes it inevitable to ensure uniform optical and scanning characteristics of each of the beams or units. Even a slight variation in mounting dimension has an adverse effect on the optical characteristics and the like, leading to the impossibility of maintaining desired characteristics. For this reason, the entire optical system is mounted to a metallic base to allow each of the optical members to remain unchanged in position.
However, the layout of optical members in a plane will cause an increase in size of the base for mounting the entire optical system thereon. Since the metallic base is costly, this will cause an increase in cost of the parts, resulting in an increase in cost of the imaging system into which such optical scanner assembly is incorporated.
In view of the aforementioned problems, the present invention provides an optical scanner assembly which can be made smaller and allows the optical members of the entire optical system to be mounted on a base such as a metallic base that can maintain the dimension thereof stable to prevent a change in mounting dimension and thus maintain the desired optical and scanning characteristics for a long time.
As technical means to achieve the object, the present invention provides an optical scanner assembly for guiding a light beam emitted from a light source into a deflector means and for allowing the light beam reflected by the deflector means to be incident upon a scanned body to scan the light beam across the scanned body. The optical scanner assembly is characterized in that part of optical members constituting the optical scanner assembly are arranged on one surface of a base having desired performance, and part of or all of the remaining members of the optical members are arranged on the other surface of the base.
The optical members are divided as appropriate to be arranged on the one and the other surfaces of the base. Accordingly, the optical path leading from the light source to the scanned body is formed across the two surfaces of the base. This structure requires a less mounting space when compared with one in which the optical path is arranged in a plane, thereby reducing the optical scanner assembly in size as well as the imaging system in which the optical scanner assembly is incorporated. In addition, since the base can be made small, the parts for the base can be prepared substantially without an increase in cost, thus preventing an increase in cost of the optical scanner assembly.
Furthermore, the optical scanner assembly mentioned above is characterized in that the light source of the optical scanner assembly and optical members of an adjustment optical system for adjusting the light beam emitted from the light source are arranged on the one surface of the base; optical members of a scanning optical system leading from the deflector means to the scanned body are arranged on the other surface of the base; and the light beam having passed through the adjustment optical system is reflected by a reflective return mirror to be guided into the scanning optical system. The optical scanner assembly mentioned above is also characterized in that the light source of the optical scanner assembly and part of the optical members of the adjustment optical system for adjusting the light beam emitted from the light source are arranged on the one surface of the base; the remaining part of the adjustment optical system and the optical members of the scanning optical system leading from the deflector means to the scanned body are arranged on the other surface of the base; and the light beam having passed through part of the adjustment optical system is reflected by the reflective return mirror to be guided into the remaining part of the adjustment optical system.
In one embodiment, a light beam emitted from the light source is adjusted to be suitable for scanning by passing through all of or part of the optical members of the adjustment optical system comprising the collimator lens, the cylindrical lens and the like, and then is incident upon the reflective return mirror. The light beam reflected by the reflective return mirror is incident upon the remaining optical members constituting the adjustment optical system or on the deflector means constituting the scanning optical system to pass through the fxcex8 lens in order to be scanned across the scanned body. These optical members are arranged across the two surfaces of the base, thereby reducing the base in size. One or a plurality of reflective return mirrors may be employed. The optical scanner assembly is also characterized in that the one surface is a front surface of the base and the other surface is the reverse surface of the base. That is, the base is substantially formed in the shape of a plate and the optical members are arranged on the front and reverse surfaces.
Furthermore, the optical scanner assembly is characterized in that a plurality of the light sources are provided, light beams emitted from the plurality of light sources are collimated to be incident upon the deflector means, and light beams reflected by the deflector means are split into a plurality of light beams and each of the light beams is scanned across each scanned body. The optical scanner assembly for use in the color imaging system scans light beams each representative of image data of four colors, that is, yellow (Y), magenta (M), cyan (C), and black (BK), across scanned bodies to form electrostatic latent images. The light sources for emitting the four light beams are arranged on one surface of the base as appropriate, and the light beams are guided into the deflector means provided on the other surface, each being scanned across each of the scanned bodies.
The optical scanner assembly is characterized in that the base is formed of metal. Since the optical members are arranged on the two surfaces of the base, the base can be reduced in size. For this reason, the base can be formed of costly metal without an increase in cost. In addition, the optical members mounted on the base can be maintained under stable conditions, thereby allowing the optical and scanning characteristics to remain in the predetermined state and thus ensuring a stable operation.
In one embodiment, the optical scanner assembly is characterized in that both surfaces of the base have mounting references for mounting the optical members thereon. Optical members to be mounted on one surface are mounted on the surface with reference to the mounting references prepared thereon. Optical members to be mounted on the other surface are mounted on the surface with reference to the mounting references prepared thereon. With optical paths to be formed on the one surface being linked with those to be formed on the other surface by means of appropriate optical link members such as the reflective return mirrors, it is possible to communicate between these optical paths. It is desirable for these optical link members to have an adjustment mechanism for linking these optical paths.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.